To control, or if necessary limit, the torque of the tool and at the same time eliminate the danger of accidents, given the ever increasing power and torque of such tools, it has been proposed in German Offenlegungsschrift No. 24 42 260 that the deformation of the handle across from the housing be measured and regulated as a function of the output of the driving motor. To measure the torque of the motor, wire strain gauges or piezoresistors are employed, which are preferably placed in an area of the tool with a reduced housing cross section.
The measurement of the housing stress in the area of the handle has the disadvantage that for every different housing construction laborious adjustment of the transducer, including the wiring, is required. Further, there is a danger that the control will not function correctly if in particular circumstances, or out of negligence, the tool is not held by the handle or if attachments to the tool reduce or prevent the handle being stressed in relation to the torque of the motor.